Sliding parts, precision parts and timepieces and electronic equipment using the same

ABSTRACT

The present invention relates to sliding parts, precision parts and timepieces and electronic equipment using those parts. Sliding parts are composed by a resin in which the degree of orientation of a fibrous filler is higher at the portion serving as the sliding surface than inside the sliding part, and the fibrous filler is oriented along the sliding surface on the sliding surface. Alternatively, precision parts are composed by a resin to which has been added carbon fibers for which a carbon compound is thermally decomposed to carbon in the vapor phase and simultaneously grown directly into fibers simultaneous to this thermal decomposition. Moreover, timepieces and electronic equipment are composed by these sliding parts or these precision parts.

TECHNICAL FIELD

The present invention relates to sliding parts, precision parts andtimepieces and electronic equipment using those parts.

BACKGROUND ART

When forming sliding parts such as gears, cams, rollers, bearings andconnectors in the past, composite materials were used that were composedby dispersing a fibrous filler such as glass fibers or carbon fibers ina matrix resin.

However, when producing sliding parts using a composite material likethat described above, the fibrous filler may end up being oriented in aspecific direction depending on the various conditions during molding(such as the shape of the molded product, locations and number of gatesprovided in the mold, viscosity and fibrous filler content of thecomposite material, and fiber length of the fibrous filler). In thiscase, anisotropy appears in the mechanical strength of the sliding part,thereby leading to problems such as being oriented in a direction inwhich there is susceptibility to the occurrence of warping in the moldedproduct, or a direction in which there is susceptibility to breaking orcracking when an external force is applied.

On the other hand, if the fibrous filler is made to not be oriented byadjusting the aforementioned molding conditions, although the appearanceof anisotropy in the mechanical strength of sliding parts as describedabove can be prevented, in this case, the majority of the fibrous fillerpresent near the sliding surface of the sliding part is facing in adirection perpendicular to the sliding surface, and since themicroscopic smoothness of the sliding surface is impaired as a result ofthis, the coefficient of friction of the sliding surface increases,thereby leading to a decrease in sliding performance.

In addition, conventional precision parts were known to be produced byusing plastic for the main plate, bridge, rotor and fifthwheel-and-pinion used in timepieces. An example of this is described inJapanese Patent No. 2962320.

However, conventional precision parts have poor transferability, andthere were discrepancies between the dimensions of the injection moldingmold and the dimensions of the part following injection molding.Consequently, extremely small parts were unable to be molded into highlyprecise shapes, and in the case of wheel-and-pinions having a smallouter diameter, there was the problem of being unable to produce theseparts using plastic to the excessively small curvature of the tip.

In addition, conventional precision parts lack smoothness and flatnessfor the surface of plastic molded products, and in the case ofthermoplastic resin in particular, there was the problem of insufficientstrength of the plastic molded parts.

DISCLOSURE OF THE INVENTION

A sliding part of the present invention is a sliding part formed by acomposite material composed by dispersing a fibrous filler in a matrixresin; wherein, the degree of orientation of the fibrous filler ishigher at the portion that serves as the sliding surface than thatinside the sliding part, and the fibrous filler is oriented along thesliding surface on the sliding surface.

In this sliding part, since the fibrous filler is oriented along thesliding surface at the portion serving as the sliding surface, differingfrom sliding parts in which fibrous filler present near the slidingsurface is not oriented, the sliding surface has a high degree ofmicroscopic smoothness, and the coefficient of friction of the slidingsurface becomes lower. In addition, since the degree of orientation ofthe fibrous filler is lower inside the sliding part than at the slidingsurface, it becomes difficult for anisotropy to appear in the mechanicalstrength of the sliding part as compared with sliding parts in which thefibrous filler contained throughout the sliding part is oriented to thesame degree as the sliding surface.

Thus, according to this sliding part, even though it is formed with acomposite material containing fibrous filler, there is no appearance ofanisotropy in its mechanical strength and sliding performance issuperior.

Furthermore, the fibrous filler present near the sliding surfacepreferably has a high degree of orientation since a higher degree oforientation results in greater precise smoothness of the slidingsurface. In addition, the fibrous filler present inside the sliding partpreferably has a low degree of orientation since the lower the degree oforientation, the lower the likelihood of the appearance of anisotropy inthe mechanical strength of the sliding part. Incidentally, among theouter surfaces of this sliding part, fibrous filler may or may not beoriented on those surfaces other than the sliding surface.

Although the amount of fibrous filler contained in the compositematerial should be suitably adjusted since it varies according to thephysical properties of the fibrous filler and the physical properties ofthe matrix resin, as a general rule, an amount of about 3% by weight to60% by weight is suitable as the weight ratio with respect to the entirecomposite material. If the amount of fibrous filler is less than 3% byweight, there are many cases in which the effect of adding the fibrousfiller is diminished excessively, while if the amount of fibrous fillerexceeds 60% by weight, there are many cases in which the continuity ofthe matrix resin is lost, thereby resulting in excessively highbrittleness.

Although a sliding part provided with the aforementioned characteristicstructure may be produced in any manner, as a specific example of this,this sliding part can be produced according to the following method.

For example, since a long fiber length facilitates orientation while ashort fiber length inhibits orientation, by suitably adjusting the fiberlength, the fibrous filler can be put into a state in which it isoriented in one portion inside the cavity, but not oriented in anotherportion. Here, since the portion where the fibrous filler is oriented isthe portion where the slippage between the matrix resin and fibrousfiller when the composite material flows within the cavity iscomparatively large, while the portion where the fibrous filler is notoriented is the portion where the aforementioned slippage between thematrix resin and the fibrous filler is comparatively small, fibrousfiller tends to be oriented easily corresponding to the amount of theincrease in flow resistance of the composite material near the innerwall of the cavity, while the fibrous filler tends to be oriented withgreater difficulty the farther away from the cavity inner wall.Consequently, simply by optimizing the fiber length of the fibrousfiller, molded products may be able to be produced in which the degreeof orientation of the fibrous filler along the sliding surface is highat the portion that serves as the sliding surface of the sliding part,while the degree of orientation of the fibrous filler is low at theportion inside the sliding part.

In addition, in addition to optimizing the fiber length of the fibrousfiller as described above, if the locations and number of gates providedin the mold, the injection pressure from the gates and so forth areadjusted corresponding to the shape of the sliding part (i.e., the shapeof the cavity inside the mold), the flow direction and flow rate of thecomposite material can be optimized so that a composite material filledinto the cavity flows rapidly in a specific direction along the slidingsurface at the portion which forms the sliding surface within thecavity. Thus, the degree of orientation of the fibrous filler in acomposite material filled into the cavity can be increased for theportion where the sliding surface is formed within the cavity.

Alternatively, as an example of a different production method, a firstcomposite material containing an easily oriented first fibrous filler(e.g., that having a long fiber length) and a second composite materialcontaining a second fibrous filler that is not easily oriented (e.g.,that having a short fiber length) may be injected into a mold cavityeither simultaneously or at a certain time difference, and the locationsof gates provided in the mold, the injection pressure from the gates,the viscosity or each composite material and so forth may be adjusted sothat mainly the first composite material flows into the portion servingas the sliding surface of the sliding part, while mainly the secondcomposite material flows into the portion serving as the inside of thesliding part. By doing so, since the first composite material containingthe easily oriented first fibrous filler is filled into the portionserving as the sliding surface of the sliding part, while the secondcomposite material containing the second fibrous filler that is noteasily oriented is filled into the inside of the sliding part, a moldedproduct can be produced in which the degree of orientation of thefibrous filler along the sliding surface is high at the portion servingas the sliding surface of the sliding part, while the degree oforientation of the fibrous filler is low inside the sliding part.

Alternatively, the step in which the portion serving as the slidingsurface of the sliding part is molded, and the step in which the insideof the sliding part is molded may be made to be separate steps, and thedegree of orientation of the fibrous filler may then be optimized foreach step. In the case of making these steps to be separate steps,either step may be carried out first. The method for optimizing thedegree of orientation of the fibrous filler in each step is arbitraryfor each step. A composite material in which the fiber length of thefibrous filler differs for each step may be used, molding conditions maybe set so that the flow rates of the composite materials within thecavity vary for each step, or both of these techniques may be used incombination.

In any case, if a sliding part is produced by these production methodsor other production methods in which the degree of orientation of thefibrous filler along the sliding surface is high at the portion thatserves as the sliding surface of the sliding part, while the degree oforientation of the fibrous filler is low inside the sliding part, eventhough it may be formed with a composite material that contains fibrousfiller, there is no appearance of anisotropy in mechanical strength andthe resulting sliding part has superior sliding performance.

However, in the sliding part explained above, the fibrous filler ispreferably composed of vapor grown carbon fibers (VGCF) having adiameter of 0.01-0.2 μm and fiber length of 1-500 μm.

In a sliding part composed in this manner, the vapor grown carbon fibersused for the fibrous filler are finer than other carbon fibers (e.g.,PAN and pitch carbon fibers). The fiber length of these vapor growncarbon fibers is preferably made to be 1-500 μm. If the fiber lengthexceeds 500 μm, the degree of orientation of the fibrous filler insidethe sliding part tends to be excessively high, while if the fiber lengthis less than 1 μm, the degree of orientation of fibrous filler near thesliding surface tends to be excessively low, thereby impairingsmoothness of the sliding surface. In addition, the diameter of thevapor grown carbon fibers is preferably made to be 0.01-0.2 μm. If thediameter exceeds 0.2 μm, the degree of orientation of the fibrous fillerinside the sliding part again tends to be excessively high, while if thediameter is less than 0.01 μm, the degree of orientation of the fibrousfiller present near the sliding surface becomes excessively low.

Since a sliding part composed in this manner is formed by a compositematerial in which the aforementioned vapor grown carbon fibers aredispersed, it demonstrates superior sliding performance in comparisonwith those using other fibrous fillers. In addition, since theaforementioned vapor grown carbon fibers are extremely fine for use asfibrous filler, enabling the fibers to enter into extremely minutesurface irregularities in the molded product, molded products can beobtained in which surface irregularities on the micron order formed inthe inner wall of the mold cavity are faithfully reproduced, and thestrength of the entire molded product, including the mechanical strengthof such minute protrusions, can be increased. Thus, the aforementionedvapor grown carbon fibers are particularly preferable in the case offorming extremely small sliding parts as well as sliding parts havingminute surface irregularities. Moreover, since they have a highcoefficient of thermal conductivity, they are also preferable for use insliding parts at locations requiring dissipation of heat, and since theyalso have a high coefficient of electrical conductivity, they also allowstatic electricity to be released when generated during sliding.

In addition, in the case of using such vapor grown carbon fibers as afibrous filler, the apparent density of the aforementioned vapor growncarbon fibers is preferably 0.05-0.1 g/cm³.

In a sliding part composed in this manner, since vapor grown carbonfibers having an apparent density of 0.05-0.1 g/cm³ are used for theaforementioned vapor grown carbon fibers, the toughness of the moldedproduct can be increased and a sliding part can be obtained that hassuperior mechanical strength. Furthermore, if the apparent densityexceeds 0.1 g/cm³, there is greater susceptibility to variations in thedispersivity in the resin. If the apparent density is less than 0.05g/cm³, since the brittleness of the molded product tends to increase, itbecomes difficult to obtain a sliding part having superior mechanicalstrength.

In addition, the aforementioned vapor grown carbon fibers are preferablyfired at a temperature of 2200-3000° C.

In a sliding part composed in this manner, since the vapor grown carbonfibers are fired at 2200-3000° C. causing the vapor grown carbon fibersto be graphitized, the solid lubricity of the sliding surface increases.In addition, graphitizing the vapor grown carbon fibers also offers theadvantage of improving electrical and thermal conductivity. Furthermore,if the firing temperature is lower than 2200° C., the vapor grown carbonfibers are not completely graphitized, resulting in the risk of adecrease in solid lubricity. In addition, if the firing temperatureexceeds 3000° C., the vapor grown carbon fibers end up decomposing,thereby making this undesirable.

Moreover, with respect to the matrix resin, the aforementioned matrixresin should be either polytetrafluoroethylene resin (PTFE), polyacetalresin (POM), polyamide resin (PA), polyethyleneterephthalate resin(PET), polybutyleneterephthalate resin (PBT), polyether ether ketoneresin (PEEK), liquid crystal polymer resin (LCP), polyphenylenesulfideresin (PPS), polycarbonate resin (PC) or polyphenylene oxide resin(PPO).

Although any of these resins should be used alone, two or more types maybe used as a mixture provided the mixture is a highly compatiblecombination or a combination in which compatibility can be enhanced by asuitable compatibility agent.

In the case of a sliding part composed in this manner, a molded productcan be obtained that is able to adequately satisfy sliding performanceand mechanical strength required by sliding parts.

In addition, the present invention also discloses precision partscomposed of a resin to which has been added carbon fibers in which acarbon compound is thermally decomposed to carbon in the vapor phase andsimultaneously grown directly into fibers simultaneous to this thermaldecomposition. Furthermore, carbon compounds such as hydrocarbons can beapplied for the carbon compound.

The present invention discloses precision parts in which carbon fibersare formed by a vapor phase-liquid phase-solid phase reaction system (tobe referred to as a VLS reaction) that proceeds in a system in whichthree phases consisting of the vapor phase, liquid phase and solid phaseare all present while using a transition metal as a catalyst.

The present invention discloses precision parts in which the carbonfibers are carbonaceous products heat treated at 1300° C.

The present invention also discloses precision parts in which the carbonfibers are graphitized products heat treated at 2800° C.

The present invention discloses precision parts in which the carbonfibers have a carbon interatomic distance (Co) of 6.9 Å, fiber diameterof 0.2 μm, fiber length of 10-20 μm, apparent density of 0.02-0.07g/cm³, true density of 1.9 g/cm³, specific surface area of 37 m²/g,hygroscopicity of 1.3%, volatile matter of 0.5-1.0%, ash content of1.5%, pH of 5 and oxidation starting temperature of 550° C.

The present invention also discloses precision parts in which the carbonfibers have a carbon interatomic distance (Co) of 6.775 Å, fiberdiameter of 0.2 μm, fiber length of 10-20 μm, apparent density of0.02-0.08 g/cm³, true density of 2.1 g/cm³, specific surface area of 15m²/g, hygroscopicity of 0.2%, volatile matter of 0.1-0.2%, ash contentof 0.1%, pH of 7 and oxidation starting temperature of 650° C.

The present invention discloses precision parts in which theaforementioned resin is at least one resin among polyacetal resin,polyamide resin, polyphenylenesulfide resin and polycarbonate resin. Asa result of using such a resin, the precision part can be used forextremely small parts in which the outer diameter of a gear molded byinjection molding is 0.2 mm, or parts such as gears having portionshaving an extremely small curvature.

In the present invention composed in this manner, the followingadvantages are obtained: (1) plastic precision parts can be made to havean extremely fine shape; (2) the end curvature of gears can be made tobe small; (3) the strength of plastic molded products is improved in thecase of thermoplastic resins; (4) wear resistance is improved; (5)transferability is improved as a result of reducing the discrepancybetween the dimensions of the injection molding mold and the dimensionsof injection molded plastic products; (6) the smoothness and flatness ofthe surfaces of plastic molded products are improved; (7) thermalconductivity is satisfactory; (8) there is no adherence of debris orfuzz; and (9) injection molded products can be obtained that have thinportions. In addition, the smallest plastic gears in the world, havingan outer diameter of 0.2 mm, can be provided by injection molding.Moreover, by utilizing these advantages in a timepiece, precision partsformed with metal materials can be reduced in weight and produced atlower costs. Moreover, by applying the present invention to the shaft ofa gear, since lubricity is imparted to the shaft, the use of lubricatingoil used for bearings along with its filling step are eliminated,thereby making it possible to realize elimination of the use oflubricating oil in a so-called timepiece assembly process. The reasonsbehind the realization of the aforementioned advantages lie in thephysical and mechanical properties of the carbon fibers used in thepresent invention including: (1) superior dispersivity in the case ofcomposing as a composite with resin since the Van der Waal's force(bonding force) between the graphite layers is weak, (2) superiortransferability to the degree that even scratches in the injectionmolding mold are transferred due to satisfactory thermal conductivity,(3) production of precision products due to superior temperaturecharacteristics, namely small coefficients of thermal expansion andthermal contraction, and (4) appearance of mechanical strength due tointeraction between the carbon fibers and resin.

The present invention also discloses a timepiece in which theseprecision parts or sliding parts are used.

In addition, the present invention discloses electronic equipmentprovided with the aforementioned sliding parts or precision parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the overall structure of aprecision part as claimed in a third embodiment of the presentinvention.

FIG. 2 is a perspective view showing the main structure of a timepieceas claimed in a fourth embodiment of the present invention.

FIG. 3 is a cross-sectional view showing the main structure of atimepiece as claimed in a fourth embodiment of the present invention.

FIG. 4 is a cross-sectional view showing the main structure of a printeras an example of electronic equipment as claimed in a fifth embodimentof the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

The following provides an explanation of examples of embodiments of thesliding parts of the present invention.

80% by weight of polyamide resin 12 (PA12) having a molecular weight of14000 and melt viscosity of 800 poise, and 20% by weight of vapor growncarbon fibers having an average fiber diameter of 0.2 μm, average fiberlength of 20 μm and apparent density of 0.07 g/cm³ pre-fired at 2800°C., were respectively weighed, kneaded and extruded into the shape of φ3mm strands at a temperature of 230° C. with a double-screw extrudingmachine followed by palletizing to obtain a raw material.

This raw material was then loaded through material feed port of aninjection molding machine, plasticized at cylinder temperatures of 210°C., 220° C., 230° C. and 220° C. in that order followed by injection ofthe aforementioned melted material into a metal mold having a cavity inthe shape of a thin plate at an injection pressure of 44 MPa andinjection rate of 100mm/s. The temperature of the metal mold was set to60° C.

After allowing a suitable cooling time to elapse, the metal mold wasopened, the material was pushed out of the metal mold with an ejectorpin and the molded product was placed in a plastic container.

The coefficient of dynamic friction of the surface corresponding to thesliding surface of the resulting molded product was 0.25 and thespecific wear rate was 3.8×10⁻¹³ mm/N·km, thereby having superiorperformance as a sliding part.

In addition, when the surface corresponding to the sliding surface ofthe resulting molded product was observed with a scanning electronmicroscope, the vapor grown carbon fibers were oriented uniaxially inparallel with the sliding surface on the surface corresponding to thesliding surface. In addition, when a plurality of cross-sections havingmutually different normal directions were observed with a scanningelectron microscope, the degree of orientation of vapor grown carbonfibers inside the molded product was lower than on the sliding surface,and the vapor grown carbon fibers were oriented in random directions.

When tensile rupture strength was measured in the same direction as areference direction and in a direction perpendicular to the referencedirection by taking the direction in which the vapor grown carbon fiberswere oriented on the aforementioned sliding surface to be the referencedirection, the tensile rupture strength was nearly equal for bothdirections.

In this manner, according to the aforementioned molded product, eventhough it is formed with a composite material containing fibrous fillerand the fibrous filler is oriented on a sliding surface, anisotropy doesnot appear in its mechanical strength, and the sliding performance ofthe sliding surface exhibits an extremely superior value.

Although the above has provided an explanation of an embodiment of asliding part of the present invention, the present invention is notlimited to the aforementioned specific embodiment, but rather can becarried out in various other modes.

For example, although polyamide resin (PA) was used for the matrix resinin the aforementioned embodiment, various other types of engineeringplastics may also be used for the matrix resin. Specific examples ofengineering plastics that can be used include polytetrafluoroethyleneresin (PTFE), polyacetal resin (POM), polyethyleneterephthalate resin(PET), polybutyleneterephthalate resin (PBT), polyether ether ketoneresin (PEEK), liquid crystal polymer (LCP), polyphenylene-sulfide resin(PPS), polycarbonate resin (PC) and polyphenylene oxide resin (PPO).

In addition, although vapor grown carbon fibers having specific physicalproperties were used for the fibrous filler in the aforementionedembodiment, any fibrous filler can be used provided the degree oforientation near the sliding surface is higher than that within thesliding part, and it is oriented along the sliding surface near thesliding surface. However, in the case there are minute surfaceirregularities in the sliding part, it is better to use a fine fibrousfiller, and vapor grown carbon fibers having a diameter of 0.01-0.2 μmand fiber length of 1-500 μm are preferable with respect to this point.In addition, in this case, the apparent density of the vapor growncarbon fibers is more preferably 0.05-0.1 g/cm³, and the vapor growncarbon fibers are more preferably fired at a temperature of 2200-3000°C.

Second Embodiment

Next, an explanation is provided of an embodiment of precision parts ofthe present invention.

Carbon fibers as claimed in the precision parts of the present inventionare carbon fibers in which a carbon compound such as a hydrocarbon isthermally decomposed in the vapor phase and simultaneously growndirectly into fibers simultaneous to this thermal decomposition. Thesecarbon fibers are formed by a VLS reaction that proceeds in a system inwhich three phases consisting of the vapor phase, liquid phase and solidphase are all present while using a transition metal as a catalyst.These carbon fibers are either carbonaceous products heat treated at1300° C. (Carbon Fiber A) or graphitized products heat treated at 2800°C. (Carbon Fiber B). Carbon Fiber A has a carbon interatomic distance(Co) of 6.9 Å, fiber diameter of 0.2 μm, fiber length of 10-20 μm,apparent density of 0.02-0.07 g/cm³, true density of 1.9 g/cm³, specificsurface area of 37 m²/g, hygroscopicity of 1.3%, volatile matter of0.5-1.0%, ash content of 1.5%, pH of 5 and oxidation startingtemperature of 550° C. Carbon Fiber B has a carbon interatomic distance(Co) of 6.775 Å, fiber diameter of 0.2 μm, fiber length of 10-20 μm,apparent density of 0.02-0.08 g/cm³, true density of 2.1 g/cm³, specificsurface area of 15 m²/g, hygroscopicity of 0.2%, volatile matter of0.1-1.2%, ash content of 0.1%, pH of 7 and oxidation startingtemperature of 650° C.

Next, an explanation is provided of the case of adding various resins tothese carbon fibers. The resins used consisted of polyacetal resin,polyamide resin, polyphenylenesulfide resin and polycarbonate resin.When the carbon fibers were added to these resins, fluidity duringinjection molding can be improved and the occurrence of shrink marks inthe molded precision parts can be decreased. For example, when carbonfibers are added to polyamide resin at 20% by weight and 40% by weight,although the coefficient of friction is 0.5 in a resin product to whichthey have not been added, the coefficient of friction in resin productsto which they have been added becomes 0.2, making it possible to improvewear resistance considerably. However, if the amount of carbon fiberadded is not suitable, gas is generated during injection molding therebypreventing injection molding from being carried out. For example, whencarbon fibers are added to polyacetal resin, gas is generated duringinjection molding if the amount added is not less than 20% by weight.Accordingly, the amount of carbon fiber added to polyacetal resin ispreferably within the range of no more than 20% by weight. An amount of20% by weight or 40% by weight is suitable when adding carbon fibers topolyamide resin. When carbon fiber is added to polyphenylenesulfideresin, resin fluidity during injection molding worsened due to theamount added not being less than 20% by weight. Accordingly, the amountof carbon fiber added to polyphenylenesulfide resin is preferably withinthe range of no more than 20% by weight.

Table 1 shows the basic characteristics of polyamide resin 12 (PA12),polyacetal resin (POM) and polycarbonate resin (PC) to which has beenadded 10% by weight or 20% by weight of the aforementioned fibrousfiller (carbon fibers). Furthermore, for the sake of comparison, anon-composite material to which fibrous filler has not been added (resinonly) is shown as a “Blank”.

Each of the aforementioned resins was injected molded according tomolding conditions as shown in Table 2. Namely, a composite material inwhich 20% by weight of fibrous filler was added to PA12 was injectionmolded at temperatures of the nozzle, front portion (weighing portion),middle portion (compressing portion), rear portion (feeding portion) andmolding mold of 220° C., 230° C., 220° C., 210° C. and 70° C.,respectively, while the same temperatures for a non-composite materialof PA12 were 190° C., 200° C., 180° C., 170° C. and 70° C.,respectively. In addition, a composite material in which 20% by weightof fibrous filler was added to POM was injection molded by setting eachof the aforementioned temperatures to 200° C., 210° C., 190° C., 170° C.and 60° C., respectively, while the same temperatures for anon-composite material of POM were set to 180° C., 185° C., 175° C.,165° C. and 60° C., respectively. Moreover, a composite material inwhich 20% by weight of fibrous filler was added to PC was injectedmolded by setting each of the aforementioned temperatures to 290° C.,310° C., 290° C., 270° C. and 80° C., respectively, while the sametemperatures for a non-composite material of PC were set to 280° C.,290° C., 270° C., 260° C. and 80° C., respectively. Furthermore, thesame conditions as in the case of addition of 20% by weight were usedfor a composite material in which 10% by weight of fibrous filler wasadded to PA12.

Here, the coefficient of dynamic friction, specific wear rate (mm³/N·km)and critical PV value (kPa·m/s) indicate values when a resin fragment ofa predetermined shape (φ55 mm×thickness: 2 mm) was slid over acopperplate (S45C) at a velocity of 0.5 m/sec while applying surfacepressure of 50 N.

Furthermore, these measurements are carried out in accordance withplastic sliding wear testing methods (JIS (Japanese Industrial Standard)K7218).

Measurement of specific gravity is carried out in accordance with thedensity and specific gravity measurement methods for plastics andnon-foam plastics (JIS K7112 (Method A)).

In addition, tensile rupture strength (MPa) refers to the tensile stressat the moment the test piece ruptures, while tensile rupture elongation(%) refers to the elongation corresponding to tensile rupture strength.

Tensile rupture strength and tensile rupture elongation are measured inaccordance with plastic tension test methods (JIS K7113) using JIS No. 1testpieces.

In addition, bending strength (MPa) and bending elastic modulus (MPa)are measured using a plastic testpiece measuring 80 mm×10 mm×2 mm, andare measured in accordance with plastic bending characteristics testingmethods (JIS K7171).

Moreover, volume resistivity (Ω·cm) is measured for a plastic testpiecemeasuring 100 mm×80 mm×2 mm using an MCP-T600 resistivity meter (LorestaGP, Dia Instruments) or MCP-HT450 resistivity meter (Hiresta UP, DiaInstruments).

Thermal conductivity (W/m·K) is measured for a plastic testpiecemeasuring 100 mm×80 mm×2 mm using the QTM-500 thermal conductivity meter(Quick Thermal Conductivity Meter, Kyoto Electronics Manufacturing).

TABLE 1 PA12 POM PC VGCF VGCF VGCF Item Units 20 wt % 10 wt % Blank 20wt % Blank 20 wt % Blank Coefficient — 0.25 0.56 0.46 0.33 0.18 0.51 ofdynamic (*brittle) friction Specific mm³/ 3.8 × 10⁻¹³ 5.2 × 10⁻¹¹ 3.3 ×10⁻⁹ 1.3 × 10⁻⁹ 3.3 × 10⁻⁸ 8.1 × 10⁻⁸ wear rate N · km Critical PV KPa ·m/s 1547 765 1056 765 1056 765 value (melt) (melt) (melt) (melt) (melt)Avg. surface nm 35.9 131.9 184.6 roughness Specific — 1.13 1.07 1.021.51 1.41 1.30 1.20 gravity Tensile MPa 56.5 49.0 41.4 60 69 rupturestrength Tensile % 16 ≧300 40 115 rupture elongation Bending Mpa 71.954.9 90 93 strength Bending Mpa 3090 1400 2580 2350 elastic modulusVolume Ω · cm 3.3 × 10³  1.4 × 10¹³ 1.2 × 10¹⁴  2.4 × 10⁰    1 × 10¹⁴1.48 × 10³ resistivity Thermal W/m · K 1.49 0.82 0.30 conductivity

TABLE 2 PA12 POM PC VGCF Blank VGCF Blank VGCF Blank Nozzle 220° C. 190°C. 200° C. 180° C. 290° C. 280° C. Front 230° C. 200° C. 210° C. 185° C.310° C. 290° C. Middle 220° C. 180° C. 190° C. 175° C. 290° C. 270° C.Rear 210° C. 170° C. 170° C. 165° C. 270° C. 260° C. Metal mold  70° C. 70° C.  60° C.  60° C.  80° C.  80° C. temperature

As shown in Table 1, in the case of PA12 and PC, composite materials towhich fibrous filler had been added exhibited improved basiccharacteristics as compared with non-composite materials not containingfibrous filler, the amount of improvement with respect to tensilerupture strength, volume resistivity and thermal conductivity was foundto increase the greater the amount of fibrous filler added.

Here, the coefficient of dynamic friction is an indicator of thesmoothness and flatness of the surfaces of the aforementioned compositematerials, and by composing a gear with a composite material having asmall coefficient of dynamic friction, for example, the gear can berotated more smoothly. In contrast to the surface roughness of PA12being about 185 nm, when fibrous filler was added at 10% by weight and20% by weight, surface roughness improved to about 132 nm and about 36nm, respectively. Surface roughness was measured with Nanopics 1000 andNPX100 desktop compact probe microscopes (Nanopics, Seiko Instruments).

In addition, the amount of improvement in volume resistivity issignificantly larger in the case of adding fibrous filler at 20% byweight than in the case of adding at 10% by weight. Volume resistivityis an indicator of the ease of acquiring an electrostatic charge, withit being more difficult to acquire an electrostatic charge the smallerthe value of volume resistivity, thereby making it more difficult fordebris and fuzz to adhere. Consequently, as a result of making thecontent of fibrous filler in the composite materials 10% by weight, theproblem of debris and so forth becoming trapped in a gear made of such acomposite material and causing equipment to operate improperly can beavoided. In addition, the effect against static electricity is even morepronounced when fibrous filler is added at 20% by weight. Moreover, inthe case of molding a composite material by injection molding, since theamount of time in which the composite material can be removed from themetal mold is dependent upon the cooling rate (namely, the ease ofcooling) of the composite material, increasing the thermal conductivityof a composite material can be expected to improve the productionefficiency of the composite material.

Furthermore, although the coefficient of dynamic friction increasesslightly in the case of a composite material in which fibrous filler isadded to POM a compared with that not containing fibrous filler, sincethere are improvements in all other basic characteristics,characteristics can be said to be improved overall.

In the present embodiment, a prototype of a timepiece gear wasfabricated by injection molding using resin to which carbon fibers hadbeen added. The fabricated timepiece gear was made to have roughly thesame level of dimensions as the dimensions of the initial drawing, andwas demonstrated to have superior transferability of the fibrousfiller-containing resin of the present invention. In addition, carbonfibers were uniformly filled into the ends and edges of the timepiecegear during molding, there was no deviation of carbon fibers in thecomposite of resin and carbon fibers within the injection moldingmachine, and the carbon fibers were determined to be uniformlydispersed. In addition, resin to which carbon fibers were added has theadvantages of being able to be purged rapidly when changing the materialduring injection molding, and there is no unused resin materialremaining in the hopper.

Third Embodiment

Next, an explanation is provided of an embodiment of precision parts ofthe present invention.

The smallest plastic gear 10 in the world having an outer diameter ofthe gear portion having six teeth of 0.2 mm was produced (see FIG. 1).PA12 was used for the resin, and carbon fibers were added at 20% byweight. When this gear 10 was assembled in a timepiece and operated, itreliably demonstrated the function of a gear. The present inventiondemonstrates that extremely small parts can be provided by resininjection molding, and is able to contribute to the reduced size oftimepiece and other precision parts. Furthermore, although Carbon FiberA was explained in the second embodiment as being a carbonaceous productthat is heat treated at 1300° C., it can be used practically provided itis a carbonaceous product that is heat treated at 1000-1500° C.Similarly, although carbon fiber B was explained in the secondembodiment as being a graphitized product that is heat treated at 2800°C., it can be used practically provided it is a graphitized product thatis heat treated at 2200-3000° C.

Fourth Embodiment

Next, an explanation is provided of an embodiment of precision parts ofthe present invention.

A main plate, a train wheel bridge, a fifth wheel-and-pinion and a rotorwere produced using a resin to which carbon fibers had been added asclaimed in the present invention.

FIGS. 2 and 3 show the essential structure of a timepiece of the presentembodiment, and each of the wheel-and-pinions 10, 20 and 30, main plate50 and train wheel bridge 60 in the form of precision parts that composethis timepiece are respectively composed of a composite material (resinto which fibrous filler has been added) as claimed in the aforementionedfirst embodiment or second embodiment. Fourth wheel-and-pinion 30, fifthwheel-and-pinion 20 and sixth wheel-and-pinion 10 compose train wheelsby meshing with gear 11 of sixth wheel-and-pinion 10 and gear 21 offifth wheel-and-pinion 20 and with gear 22 of fifth wheel-and-pinion 20and gear 31 of fourth wheel-and-pinion 30, and shafts 10 a through 30 aon the side of train wheel bridge 60 of each wheel-and-pinion 10 through30 are rotatably supported by bearings 10 b through 30 b of train wheelbridge 60, respectively. In addition, shafts 10 c through 30 c on theside of main plate 50 of each wheel-and-pinion 10 through 30 arerotatably supported by bearings 10 d through 30 d of main plate 50,respectively. This train wheel is rotated by a stepping motor (notshown) that drives sixth wheel-and-pinion 10 so as to rotate second hand40 attached to fourth wheel-and-pinion 30. Furthermore, train wheelbridge 60 is fastened to main plate 50 by screw pin 70 and screw 80.Moreover, dial 90 is fastened to main plate 50 by press-fitting theprotrusion (not shown) of dial 90 into an indentation (not shown) inmain plate 50.

The dimensions of these precision parts were made to be nearly at thesame level as the dimensions shown in the drawings. In addition, therewas found to be no adherence of debris or fuzz to those parts in whichcarbon fibers were added to the resin, and those parts were determinedto function normally. In addition, with respect to durability as well,when these parts were assembled in the timepiece, fifth wheel-and-pinion20 and the rotor were able to rotate despite not applying lubricatingoil. Moreover, even when rotated 100,000 times, the timepiece was ableto run and there was no wear of parts. Thus, the use of parts in whichcarbon fibers have been added to the resin makes it possible to producea timepiece that can run without the application of lubricating oil. Asa result, the need for a lubrication step in the production process iseliminated, and the need for a lubrication step during maintenance canalso be similarly eliminated. In addition, since lubrication steps arenot required, the use of lubricating oil can be discontinued, therebyoffering the advantage of lowering production costs. Moreover, there isalso the advantage of the timepiece not being caused to stop running dueto the presence of debris or fuzz.

Fifth Embodiment

The following provides an explanation of an embodiment of precisionparts or sliding parts of the present invention.

Gears 100 and 150 and bearing 120 were produced in the form of slidingparts or precision parts from a composite material in which a fibrousfiller was added to a resin as claimed in the present invention, and aprinter was produced as shown in FIG. 4 using these gears.

FIG. 4 is an enlarged view of the drive mechanism of a printer. Shaft110 of roller 130 is rotatably attached to frame 200 by bearing 120composed of the composite material as claimed in the aforementionedfirst embodiment or second embodiment (resin to which has been added afibrous filler), and gear 100 composed of the aforementioned compositematerial is provided on the end of that shaft. Gear 150 composed of theaforementioned composite material meshes with this gear 100, and roller130 is rotated by driving this gear 150 with a drive motor (not shown).

Since the printer of the present embodiment uses gears 100 and 150 aswell as bearing 120 composed of the aforementioned composite materialfor the drive mechanism that drives roller 130, the adherence of debrisand fuzz, etc. to the meshing portions of these gears 100 and 150 aswell as to bearing 120 can be prevented, and the rotary driving ofroller 130 can be carried out smoothly without using lubricating oil.

Furthermore, the present invention is not limited to the aforementionedembodiments, but rather can be modified in various ways within a rangethat does not deviate from the gist of the present invention.

For example, although gears were indicated as examples of precisionparts or sliding parts in the aforementioned second through fifthembodiments, the aforementioned composite material can also be appliedto other shafts and bearings such as shafts, bearings, guides andhinges, mechanical parts used to transfer rotary power such as chains,belts, cams and rollers, as well as rotating mechanical products such asgear pumps.

INDUSTRIAL APPLICABILITY

In the sliding parts of the present invention, since a fibrous filler isoriented along the sliding surface in the portion serving as the slidingsurface, differing from parts in which fibrous filler present near thesliding surface is oriented, the sliding surface has a high degree ofmicroscopic smoothness, and the coefficient of friction of the slidingsurface becomes lower. In addition, since the degree of orientation ofthe fibrous filler is lower inside the sliding part than at the slidingsurface, it becomes difficult for anisotropy to appear in the mechanicalstrength of the sliding part as compared with sliding parts in which thefibrous filler contained throughout the sliding part is oriented to thesame degree as the sliding surface.

Thus, according to this sliding part, even though it is formed with acomposite material containing fibrous filler, there is no appearance ofanisotropy in its mechanical strength and sliding performance issuperior.

In addition, as was previously explained, according to the presentinvention, the following advantages are obtained: (1) parts can be madeto have an extremely fine shape; (2) the end curvature of gears can bemade to be small; (3) the strength of plastic molded products isimproved in the case of thermoplastic resins; (4) wear resistance isimproved; (5) transferability is improved as a result of reducing thediscrepancy between the dimensions of the injection molding mold and thedimensions of injection molded plastic products; (6) the smoothness andflatness of the surfaces of plastic molded products are improved; (7)thermal conductivity is satisfactory; (8) there is no adherence ofdebris or fuzz; and (9) injection molded products can be obtained thathave thin portions. In addition, the smallest plastic gears in theworld, having six teeth and an outer diameter of 0.2 mm, can be providedby injection molding. Moreover, by utilizing these advantages in atimepiece, precision parts formed with metal materials can be reduced inweight and produced at lower costs. Moreover, by applying the presentinvention to the shaft of a gear, since lubricity is imparted to theshaft, the use of lubricating oil used for bearings along with itsfilling step are eliminated, thereby making it possible to realizeelimination of the use of lubricating oil in a so-called timepieceassembly process.

1. A sliding part formed by a composite material comprising a fibrousfiller dispersed in a matrix resin; wherein, the degree of orientationof the fibrous filler is higher at the portion that serves as thesliding surface than that inside the sliding part, and the fibrousfiller is oriented along the sliding surface on the sliding surface, andthe fibrous filler consists of vapor grown carbon fibers having thedensity of 0.05-0.1 g/cm³.
 2. The sliding part according to claim 1wherein, the vapor grown carbon fibers have a diameter of 0.01-0.2 μmand a fiber length of 1-500 μm.
 3. The sliding part according to claim 1or 2 wherein the matrix resin is either polytetrafluoroethylene resin,polyacetal resin, polyamide resin, polyethylene- terephthalate resin,polybutyleneterephthalate resin, polyether ether ketone resin, liquidcrystal polymer resin, polyphenylenesulfide resin, polycarbonate resinor polyphenylene oxide resin.
 4. A timepiece equipped with sliding partsaccording to any of claims 1 and
 2. 5. Electronic equipment equippedwith sliding parts according to any of claims 1 and
 2. 6. The slidingpart according to claim 2, wherein the vapour grown carbon fibers arefired at a temperature of 2200-3000° C. and are graphitized.